INTRODUCTION The objective of this study was to quantify the acute and long term effects of needle puncture injury on mouse caudal disc mechanical properties, disc height and glycosaminoglycan (GAG) content. We hypothesize that puncture injury will cause a deficiency in mechanical function and these changes will be amplified over time. METHODS Surgery: The (caudal) C6/C7 and C8/C9 discs were either exposed and punctured with a 29G needle (≈65% disc height) or exposed as an intact sham control. The needle was clamped and inserted 1.75 mm to ensure full penetration of the adjacent annulus. Mechanical Testing: Spines were then separated into motion segments, equilibrated in PBS and 4oC overnight and tested in tension/compression (20 cycles: +0.5 N, -1.5N, 0.025 Hz), creep (-1.5 N, 1 hour), and torsion (10 cycles: +/-8o, 0.05 Hz) on an Instron 5542 mechanical testing system equipped with a custom torsional testing device. The device is composed of a stepper motor in series with a torque cell and two digital cameras to track the extension and rotation of each motion segment. Total range of motion (ROM), creep displacement, and torsional stiffness were calculated from the raw data. All mechanical parameters were normalized to disc geometry: total ROM and creep displacement were multiplied by 1/h while torsional stiffness was multiplied by h/Jz. RESULTS As a result of injury, mean disc height decreased by 19% after eight weeks, matching a nonsignificant loss of GAG content over the same period. In addition, total ROM increased 32% eight weeks after injury, though the sham treatment had a significant effect on total ROM as well. Creep displacement increased 34% after eight weeks. There were no changes in torsional mechanics and there were no differences between sham and treatment groups with puncture/time.
Listed In: Biomechanical Engineering, Biomechanics, Mechanical Engineering, Orthopedic Research